Transcript Big Idea #1
BIG IDEA #1 The process of evolution drives the diversity and unity of life. MECHANISMS OF VARIATION Natural selection acts on phenotypic variations in populations Sources of variation: Mutation Random assortment during meiosis Crossing Over Random Fertilization Diploidy Allele Frequencies can be altered by: Gene Flow: Immigration and Emigration Genetic Drift: small populations Mating Patterns: Inbreeding and Sexual Selection T YPES OF SELECTION Stabilizing Selection: favors intermediate phenotype (heterozygote advantage) Directional Selection: favors one extreme over another Disruptive Selection: favors both extremes over the intermediate Campbell, Neil A. Reece; Jane B., BIOLOGY, 6th Edition 2002 PATTERNS OF EVOLUTION Convergent Evolution: two dissimilar populations evolve similar traits b/c of similar selective pressures. Ex: dolphin and shark Parallel Evolution: similar to convergent however, organisms do not need to occupy the same niches. Ex: warning colors of many organisms Divergent Evolution: organisms from a common ancestor become less similar (adaptive radiation) Ex: Galapagos Tortois EVIDENCE FOR EVOLUTION DNA Amino acid sequence/similar proteins Analogous structures Vestigial structures Homologous structures CONDITIONS FOR HARDY-WEINBERG EQUILIBRIUM Large population Random mating No mutations No gene flow No natural selection DETERMINING ALLELE FREQUENCIES Frequency of dominant allele if frequency of recessive allele is given p if q is given Frequency of recessive allele if the % of the population with the recessive phenotype is given q if q 2 is given Calculate the % of the population with recessive allele if the % of the population expressing the dominant allele is given q 2 if p 2 +2pq SPECIATION Speciation occurs when populations accumulate enough changes over time to lead to the emergence of a new species. Types: Allopatric—geographic barriers Sympatric—reproductive barriers Polyploidy in plants leads to new species b/c the polyploids can not breed with the diploid ancestors MECHANISMS FOR REPRODUCTIVE ISOLATION Prezygotic Isolating Mechanisms: Geographic (Habitat) Isolation Ecological Isolation Behavioral Isolation Temporal Isolation Mechanical Isolation Sexual Isolation Postzygotic Isolating Mechanisms: Hybrid Sterility Hybrid Inviability Zygote Mortality PRE AND POST ZYGOTIC MECHANISMS FOR REPRODUCTIVE ISOLATION ORIGINS OF LIFE Miller and Urey’s Experiment Amino acid monomers, polymers, protobiont, first cells Characteristics of the First Cells Unicellular Heterotrophic Prokaryotic Simple lipid membrane Ribosomes RNA Autotrophic prokaryotes would appear soon after ORIGINS OF COMPLEX CELLS Theory of Endosymbiosis — Large eukaryotic cells evolved when a small prokaryotic cells was engulfed by a larger prokaryotic cell and they developed a symbiotic relationship where both benefitted. Smaller one eventually evolves into mitochondria (in heterotrophs) or chloroplasts (in autotrophs). Evidence: Mitochondria and Chloroplasts have their own DNA and ribosomes. They are about the size of prokaryotes. Their membranes are similar to prokaryotes. DIVERSIT Y OF LIFE Three Domains Bacteria Archae Eukarya Six Kingdoms Eubacteria Archaebacteria Protista Fungi Plantae Animalia CLADOGRAMS Cladograms show relative relatedness between a group of organisms